1. Field of the Invention
The present invention relates to an optical head and an optical pickup having an optical head.
2. Description of the Related Art
U.S. patent application Ser. No. 09/336,505 shows an invention of a chromatic aberration correcting element and an optical pickup apparatus provided with it.
It is desired to shorten a wavelength of an output light beam of a light source of an optical pickup in order to increase the storage capacity of an optical disc. For example, for a compact disc (CD), the wavelength of the output light beam of the laser diode is about 780 nm, while for a digital versatile disc (DVD), which has a larger storage density than a CD, the wavelength of the output light beam of the laser diode is about 650 nm.
Recently, mounting of a laser diode (LD) emitting a blue or blue-violet laser beam of about 405 nm wavelength to an optical pickup is being considered.
When the wavelength of a laser diode is made shorter than 450 nm, generally a lens easily gives rise to chromatic aberration. Therefore, it is preferable to arrange an achromatic lens for correcting the chromatic aberration on the optical path so as to cancel the chromatic aberration of said lens.
An object of the present invention is to provide an optical head having an achromatic lens and an optical pickup having this optical head.
A first optical head according to the present invention has an achromatic lens which a laser beam strikes, an object lens for condensing said laser beam passing through said achromatic lens on an optical disc, a lens holder for holding said achromatic lens and said object lens so that their optical axes coincide, and an actuator for moving said lens holder which holds said achromatic lens and said object lens in a focus direction and/or tracking direction of said optical disc.
In the first optical head according to the present invention, preferably said lens holder comprises a first lens holder for holding said achromatic lens and a second lens holder for holding said object lens, and said first and second lens holders are fixed to each other so that optical axes of said achromatic lens and said object lens coincide or substantially coincide.
In the first optical head according to the present invention, preferably said laser beam striking said achromatic lens is a blue or blue-violet laser beam output from a laser diode.
A second optical head according to the present invention comprises an achromatic lens which a laser beam strikes, an object lens for condensing said laser beam passing through said achromatic lens on an optical disc, a first actuator for moving said achromatic lens and said object lens in a tracking direction of said optical disc, and a second actuator for moving said object lens, among said achromatic lens and said object lens, in a focus direction of said optical disc.
The second optical head according to the present invention preferably comprises a first lens holder for holding said achromatic lens, a second lens holder for holding said object lens, and an elastic member interposed between said first lens holder and said second lens holder.
In the second optical head according to the present invention, preferably said laser beam striking said achromatic lens is a blue or blue-violet laser beam output from a laser diode.
A first optical pickup according to the present invention comprises a laser, an optical head for condensing a laser beam from said laser on an optical disc, and a photodetector for receiving said laser beam reflected at said optical disc, wherein said optical head has an achromatic lens which said laser beam from said laser strikes, an object lens for condensing said laser beam passing through said achromatic lens on said optical disc, a lens holder for holding said achromatic lens and said object lens so that their optical axes coincide, and an actuator for moving said lens holder which holds said achromatic lens and said object lens in a focus direction and/or tracking direction of said optical disc.
In the first optical pickup according to the present invention, preferably said lens holder comprises a first lens holder for holding said achromatic lens and a second lens holder for holding said object lens, and said first and second lens holders are fixed to each other so that optical axes of said achromatic lens and said object lens coincide or substantially coincide.
In the first optical pickup according to the present invention, preferably, said laser is a laser diode generating a blue or blue-violet laser beam.
A second optical pickup according to the present invention has a laser, an optical head for condensing a laser beam from said laser on an optical disc, and a photodetector for receiving said laser beam reflected at said optical disc, wherein said optical head has an achromatic lens which said laser beam from said laser diode strikes, an object lens for condensing said laser beam passing through said achromatic lens to said optical disc, a first actuator for moving said achromatic lens and said object lens in a tracking direction of said optical disc, and a second actuator for moving said object lens between said achromatic lens and object lens in a focus direction of said optical disc.
In the second optical pickup according to the present invention, preferably said optical head comprises a first lens holder for holding said achromatic lens, a second lens holder for holding said object lens, and an elastic member interposed between said first lens holder and said second lens holder.
In the second optical pickup according to the present invention, preferably said laser is a laser diode generating a blue or blue-violet laser beam.
In the above described first and second optical heads according to the present invention, since the object lens condenses a laser beam passing through an achromatic lens for correcting chromatic aberration on an optical disc, the chromatic aberration of the object lens can be reduced and it is possible to improve the performance of an optical head.